The present invention relates to an air bag composed of resin sheets and its production method. The purpose of an air bag device is to protect an occupant by deploying an air bag when a vehicle comes into collision.
Conventionally, an air bag is typically made of a woven textile of fiber, such as a polyamide fiber, surfaced with a silicone rubber coating. In recent years, however, an air bag made of heat resisting resin sheets (Japanese Unexamined Patent Publication No. H2-31965/1990) and an air bag made of elastomer (Japanese Unexamined Patent Publication No. H4-266544/1992) have been proposed as alternatives to the conventional air bag.
The joint between heat resisting resin sheets and the joint between elastomer sheets are made by adhesion using adhesives or heat fusion in prior arts.
Joining by adhesion or heat fusion may bulk up the joint between the sheets or lower the strength due to heat.
It is an object of the present invention to provide a production method of an air bag made of resin for preventing the periphery from bulking up, providing sufficient joint strength between resin sheets, and providing sufficient strength to peripheries of the resin sheets.
It is another object of the present invention to provide an air bag made of resin having a means for discharging gas in the radial direction of the air bag.
A method of the present invention for producing a resin air bag composed of two resin sheets, namely, a first resin sheet and a second resin sheet, which are bonded to each other at the peripheries thereof. The method may comprise steps of: disposing the first resin sheet in a mold and superposing a heat resisting sheet having smaller size than that of the first resin sheet onto the first resin sheet to expose the periphery of the first resin sheet out of the heat resisting sheet; and injecting resin into the mold in such a manner as to cover the exposed periphery of the first resin sheet and the heat resisting sheet to form said second resin sheet. The injected resin may well adhere to the first resin sheet so that the injected resin adheres to the periphery of the first resin sheet.
In the aforementioned production method, the second resin sheet is composed of the resin injected into the mold and the resin adheres to the periphery of the first resin sheet. The first resin sheet is covered by the heat resisting sheet besides at the periphery thereof so that the injected resin does not come into contact with the covered portion of the first resin sheet. Therefore, the sheets are not bonded to each other over the covered portion. If the heat resisting sheet is provided with at least one extended portion extending outwardly, the first resin sheet and the second resin sheet are not bonded to each other also over the extended portion.
When the extended portion extends to a peripheral end of the first resin sheet, there is a non-bonded portion between the sheets over the extended portion. The non-bonded portion functions as a vent hole which allows gases introduced into the air bag to flow outside of the air bag.
When the extended portion does not extend to the peripheral end of the first resin sheet, the first and second resin sheets are bonded to each other at the peripheries thereof outside the extended portion. When the air bag is deployed, since the width of the bonded portion is slight, the sheets at this portion are separated from each other due to gas pressure introduced from an inflator in such a manner as to form a vent hole.